ctf: Make LttngKernelTraceGenerator also generate UST test traces

LttngKernelTraceGenerator can currently only generate Kernel traces
but with a few changes, it can generate a UST trace. The events do
not make much sense for a UST trace but this is good enough for trace
type validation, etc.

Change-Id: I9826383c6d3cb2bdcb24895bbfa9990a75312a4b
Signed-off-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/79780
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>